Any visual scene can be decomposed into a set of sinusoidal gratings of the appropriate spatial frequencies and orientations. Therefore, to understand visual perception in normal human observers, one should understand how relatively simple visual patterns, such as sinusoidal gratings of different spatial frequencies, are processed by the visual system. The proposed experiments are designed (1) to study the high spatial frequency cutoff to photopic visual patterns presented in the peripheral visual field; (2) to provide fundamental information about the capabilities of tje vosia; suste, accurately to perceive stimuli of high spatial frequencies; (3) to provide more information about the spacing of the inner segments of cone receptors in the periphery, and (4) to determine if distortions due to aliasing can occur in the peripheral visual field. Aliasing is the phenomenon by which a high frequency stimulus input is distorted by the system to produce a lower frequency output that lacks the original high frequency. The proposed experiments utilize psychophysical methods with human observers. The observer is asked (1) to detect the presence of a simple visual pattern, (2) to discriminate a vertically-oriented pattern from a horizontally-oriented one, or (3) to determine whether a foveally-viewed stimulus has a higher or lower apparent spatial frequency than one viewed peripherally. Theoretical predictions based on computer simulations will be compared to the empirical results obtained from human observers. Much remains to be learned about how the arrangement of cone inner segments in the periphery of the human eye affects spatial frequency perception. Moreover, little is yet known about how perceived spatial frequency in the periphery compares to that in the fovea for any given frequency. Understanding the perceptual capabilities of the normal, health visual system is necessary in order to understand the ways in which the visual system malfunctions under various pathological conditions.